Physics question

Question

A 11 kg block is slide from a height of 11.7 m down a friction-less incline. It comes to a flat surface and crosses a 8.1 m strip of sandpaper with a coefficient of friction of 0.11. After passing over the sandpaper, the block is traveling on a friction-less surface again. How fast is the block traveling? 

Answer 1

steps of the solution

1- calculate kinetic energy of the block at the time it reaches the friction surface KE 1 =m.g.h = 11x9.8x11.7 =1261.26 joule

2- calculate the loss in KE after passing the friction surface = work done by the friction force = F friction X d

F friction = μ ( coefficient of friction ) x N (reaction force on the block) =μx mg = 0.11x 11x 9.8=766.46 joule

3- Calculate the remaining KE 2= KE1 - work done by friction =1261.26 - 766.46 = 494.8 j

4-calculate the velocity of the block using KE2 = 1/2 mv² , v=√90 m/s

(write the unit near numbers , take care of significant figures as wanted in the question )